Conventionally, a mechanical cam has long been used as a means for converting the rotating movement of a spindle driven by a motor, etc., to cyclical linear movement of a driven shaft. However, if, in the case of a mechanical cam, the shape of a certain cam is determined, only one type of a cyclical displacement curve (cam linear diagram) can be obtained. In order to obtain different displacement curves, it is necessary to produce a mechanical cam having a different shape to acquire a different certain displacement curve and then replace the cam with a mechanical cam of a different shape. Therefore, a great deal of preparation time has been required for production, replacement and adjustment thereof. Recently, as a means for reducing such labor and time, an electronic cam type servo system has been developed, in which a drive shaft is also driven by a servo motor, and the servo motor is controlled and driven on the basis of instructions coming from a memory section in which position data of displacement curves are stored, whereby the driven shaft is displaced in compliance with a desirable displacement curve to correspond to different displacement curves by replacing the data of the displacement curves in the memory section.
FIG. 4 is a block diagram of a control device for a prior art servo system using an electronic cam. The data inputting and processing unit 21 in a personal computer 2 receives necessary data from input devices such as a keyboard, mouse, etc., indicated by reference number 1 and from the CRT, and edits cam data in the data editing section 22. The corresponding data may be calculated by a means not described above and may be inputted by a means such as an Excel file, etc. The edited cam data are transmitted to a data display section 25 and are converted to data displayable in the form of a table or graph (cam linear diagram, etc.). And, the data are transmitted to the CRT1 by a transmission means (not illustrated) and displayed thereon. Further, the data are converted, by a cam data converting and processing section 23, to a format by which the mechanical drive section can bring about cam actions, and are further stored in a peripheral device (a hard disk) via a cam data input/output processing section 24 by which the cam data can be stored and loaded.
In connection with the detailed preparation of cam data and sequential procedures of displaying the same in the form of graphs, first, mechanical specifications as shown in FIG. 5(a), and motor specification data are inputted by the keyboard 1 as parameters necessary for calculation. As corresponding data, database linked with the types of motors may be utilized. At this time, premised conditions for cam design as shown in FIG. 5(b) are established as cam data specifications to be prepared, and are stored in a work memory of the personal computer 2.
Based on the cam data specification in FIG. 5(b), the data editing section 22 prepares, as one example of a displacement curve, a graph showing the relationship between spindle motion angles and the amount of mechanical motion, which is shown in FIG. 6. Based on the cam data specifications, the graph shows a deformed sine pattern in which the ordinate indicates the amount of mechanical motion per cycle, using six divisions in a range from 116,736 pulses to the upper limit of 120,000 pulses, and the abscissa indicates the spindle motion angles, using a graduation of 0 through 22.5 degrees, wherein, for example, an instruction of a servo motor equivalent to the displacement data per rotation of a mechanical cam and corresponding thereto is expressed, and this is called a "displacement curve diagram" (displacement curve). Also, if speed is taken as the ordinate, this is called a "speed linear diagram", and if acceleration is taken as the ordinate, this is called a "acceleration linear diagram". These are generally called "cam linear diagrams".
Next, based on setting of the cam data specifications in FIG. 5(b), the data are divided into 120 sections, and differences between the respective data of the amounts of mechanical motions adjacent to each other are taken, the time acquired by dividing the time of one cycle=tc by the number of data, 120, is used, whereby 1/120 cycles is regarded as one block unit, and the speed per block can be calculated. Using the data, a graph showing the relationship between the spindle motion angles and the mechanical motion speed is prepared as in FIG. 7. These cam linear diagrams maybe subjected to further detailed modifications in compliance with the motion of a machine, the finished states of products, etc.
120 data as shown in FIG. 6 and FIG. 7 are the cam data processed in the inputting and processing section 21 and edit by the data editing section 22, and the data displaying section 25 executes a data display process in which it converts the data to correspond to an ordinate and abscissa and displays a cam linear diagram as a graph on the CRT 1 as shown in the drawings.
Finally, as one more process, the final judgement is carried out by using the following three expressions for whether or not the motor can operate with respect to the entirety of the prepared cam data.
(1). A process for judging whether or not the effective torque calculated in connection with the entirety (entire blocks) of the cam data using the prepared data is smaller than the rated torque of the motor is carried out. The effective torque Trms (Torque root means square) is obtained by the following expression (1): EQU Trms=[{(T.alpha..sub.1.sup.2.times.t.sub.1)+(T.alpha..sub.2.sup.2.times.t. sub.2)+ . . . (T.alpha..sub.m.sup.2.times.t.sub.2)}/tc].sup.1/2 (1)
wherein tm is a zonal time, and tc is the time required per cycle.
(2). Next, a process for judging whether or not the acceleration and deceleration peak torque of the respective blocks, which is calculated by using the prepared cam data, is smaller than the maximum instantaneous torque of the motor is carried out after the acceleration and deceleration peak torque TQ is obtained by the following expression (2): EQU T.alpha.=(GD.sup.2.sub.L +GD.sup.2.sub.M)/375.times.{N(m)-N(m-1)}/tm (2)
where N(m) and N(M-1) are zonal speeds (pulse values).
(3). Judgement as to whether or not the number of revolutions of the entirety of the respective blocks calculated by using the prepared cam data exceeds the number of revolutions of the motor is carried out. The number (NB) of times of revolutions of the blocks is obtained by the following expression (3): EQU NB{(m)-(m-1)}=N(m)-N(m-1) (3)
The final judgement is carried out by manual calculations or calculation using a separate calculation table program, etc., on the basis of the calculations made by the abovementioned expressions (1), (2) and (3), and comparison between the results of the calculation of the respective expressions and the motor specifications.
However, in the abovementioned prior art example, a great deal of time is required in the procedures for performing a re-examination where the prepared cam data are amended at site since a series of calculations are composed of many steps, wherein labor and time are excessively required for design and adjustment, thereby resulting in a problem in that it is hard to shorten the preparation time.